This invention relates to a control system using a model of a subject to be controlled, and particularly to a model-based control method and apparatus using an inverse model, suitable for controlling the air-fuel ratio of an engine.
Heretofore, a control system using a map has been employed for controlling the air-fuel ratio of an electrically controlled engine, for example. The map is made by collecting data related to a fuel-injection quantity at a certain engine speed and throttle angle, and storing the data in a memory. In actual use, an appropriate air-fuel ratio is determined by detecting an engine speed and a throttle angle, inputting the detected data into the map, determining a fuel-injection quantity based on the map, calculating a compensation most suitable for the operational conditions at the moment or determining the compensation using another map, and inputting the compensation as an actuating value into a drive apparatus system.
However, although an appropriate air-fuel ratio can be obtained by using the control system using a map if operational conditions are normal (i.e., a stable state), it is impossible to conduct appropriate air-fuel ratio control if operational conditions are transient (i.e., a transient state), wherein a throttle angle is changed due to acceleration or deceleration. In the above, after a throttle angle is changed, the change is detected, thereby controlling the air-fuel ratio, and thus, a controlled variable cannot appropriately be determined in accordance with the air or fuel flow. Thus, the control system using a map does not work when the operational state is transient.